Question

The mechanism of action of methimazole used to treat hyperthyroidism is

• A. It blocks the release of stored thyroid hormone from the gland.
• B. It replaces deficient thyroid hormone in the bloodstream.
• C. It inhibits thyroid peroxidase, reducing synthesis of thyroid hormones.
• D. It destroys thyroid tissue through radiation.

Hint:

Methimazole treats hyperthyroidism by inhibiting thyroid peroxidase and reducing new thyroid hormone synthesis.

Answer 1

The Correct Option is C

Concept:
Methimazole is an antithyroid drug used in the treatment of hyperthyroidism.

Step 1: Understanding hyperthyroidism.
Hyperthyroidism occurs when the thyroid gland produces excessive thyroid hormones, mainly \(T_3\) and \(T_4\).

Step 2: Role of thyroid peroxidase.
Thyroid peroxidase is an enzyme required for iodination of tyrosine residues and coupling reactions in thyroid hormone synthesis.

Step 3: Action of methimazole.
Methimazole inhibits thyroid peroxidase. As a result, synthesis of new thyroid hormones decreases. \[ \text{Methimazole} \Rightarrow \text{thyroid peroxidase inhibition} \Rightarrow \downarrow T_3, T_4 \text{ synthesis} \]

Step 4: Checking other options.
Blocking release of stored hormone is not the main action of methimazole.
Replacing deficient hormone is the action of levothyroxine.
Destroying thyroid tissue through radiation is the action of radioactive iodine.

Step 5: Final answer.
Therefore, methimazole inhibits thyroid peroxidase and reduces thyroid hormone synthesis. \[ \boxed{\text{It inhibits thyroid peroxidase, reducing synthesis of thyroid hormones.}} \]